<p>Calculates the difference between the value of a quantity in one point and the value of the
same quantity in another point across a basin. 
</p>
<br>
<br>
<h3>Inputs</h3>
<ol>
<li> The !GridCoverage of the drainage directions, obtained with [Markoutlets]);</li>
<li> The !Gridcoverage containing the date on which estimating the difference;</li>
<li> The !Gridcoverage containing the quantity of which calculating the difference;</li>
</ol>
<br>
<br>
<h3>Output</h3>
<ol>
<li> The !GridCoverage with the differences;</li>
</ol>
<br>
<br>
<h3>Notes</h3>
<p>
The points in which calculating the difference are
individuated by an opportune matrix. Typically this matrix could contain the values of the Strahler
numbers of a net, i.e. the network pixels are labeled by the stream number and the same stream
contains a group of subsequent pixel. The points chosen for the calculation of the difference are
the ﬁrst and the last of any stream, i.e. those in which the numeration changes.
 </p>
<p>
If the matrix of the quantity to calculate is that of elevations, then, again in the case shown, netdiff calculates the elevation
difference along a Strahler branch. If instead of the ﬁle containing the Strahler numeration the matrix
of the magnitude is used, the variation of a quantity in a link is measured.
</p>
<br>
<br>
<h3>References</h3>
<ul>
<li> [Bibliography#8, 8] I. Rodriguez-Iturbe, 1997</li>
<li> [Bibliography#9, 9] M.J. Woldenborg, 1982</li>
</ul>